1. Field of the Invention
This invention relates to fail-safe computer systems and particularly to such systems in which a slave computer or microprocessor monitors the operation or of a master computer or microprocessor and outputs an error condition signal when an error is detected.
2. Discussion of Related Art
It has become quite common to use redundant processors to provide a fail-safe mode of operation. The master processor executes programs and the slave processor mimics the operation of the master processor. The slave receives the same inputs as the master and has its output drivers disabled. The output pins of the slave are connected to the master's. By comparing the internally generated input to its output drivers to the outputs of the master processor, the slave performs a comprehensive check of the operation of the master processor. If a discrepancy is detected, an error signal is generated.
A master/slave combination can operate properly for years before an error condition is encountered. During this period, it would be desirable to determine if the master/slave configuration is performing its proper error monitoring function. However, presently, there is no known system or method for checking the error detecting operation of a master/slave combination within a simple master/slave checking system such as used in the AM 29000 microprocessor produced by Advanced Micro Devices of Sunnyvale, Calif., where the slave snoops the master output.